In transistor fabrication, in the past, aluminum has been widely used as silicon dopant to create P well structures in Si. Aluminum works well for this application because it rapidly diffuses into silicon. Aluminum may also be used to dope copper in order to reduce electro-migration in dual damascene copper lines for instance.
Lavoie et al. (US20080241575) describes the use of various aluminum precursors to dope copper. Aluminum is deposited on top of a metallic structure and the Aluminum diffuses into the film during an annealing step. Methylpyrrolodinealane (MPA), Aluminum s-butoxide, trimethylaluminum (TMA), Triethyl aluminum, di-1-butylaluminum chloride, di-1-butylaluminum hydride, diethylaluminum chloride, tri-1-butylaluminum and trimethyl(tri-sec-butoxy)aluminum are among the claimed aluminum precursors. Other claimed compounds include H3Al, H3Al:L or H(R)2Al:H wherein R is an alkyl or a perfluoroalkyl and L is a Lewis base.
Medulla et al. (U.S. Pat. No. 5,497,005) present the use of Alumina (Al2O3) as source material for Al doping by creating a stream of ionic Aluminum. Al2O3 is a solid that is challenging to deliver into a chamber in a gas phase. Moreover, Oxygen containing molecules should avoided if possible because of oxidation of the walls of deposition chambers and the difficulty in desorption of such molecules.
Kensuke et al. (JVSTA 16(2), March/April 1998) described the use of AlCl3 for high energy ion implantation using a variable energy radio frequency quadrupole implanter. Al2+ implantation is carried out at energy of 0.9 MeV and 1.0 MeV with doses of 1×1014 cm−2 and 1×1016 cm−2. However, they state that temperature needs to be carefully controlled in order to have stable ion beams and therefore uniform implantation of the wafers (the vapor pressure of AlCl3 being only 1 Torr at 100 C).
Shibagaki (US20090190908) suggest the use of TMA (Trimethylaluminum) for aluminum implantation. However, TMA is a highly pyrophoric gas meaning that specific safety devices and procedures are needed to handle the gas.